U.S. patent application number 10/699539 was filed with the patent office on 2004-07-15 for liquid crystal display device and electronic device.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Maeda, Tsuyoshi.
Application Number | 20040135949 10/699539 |
Document ID | / |
Family ID | 32716069 |
Filed Date | 2004-07-15 |
United States Patent
Application |
20040135949 |
Kind Code |
A1 |
Maeda, Tsuyoshi |
July 15, 2004 |
Liquid crystal display device and electronic device
Abstract
The present invention provides a high-contrast reflective
display and transmissive display with a wide viewing angle in a
transflective liquid crystal display device having reflective and
transmissive structures. In such a display, each of dots can
contain a reflective display region for reflective display and a
transmissive display region for transmissive display. A liquid
crystal layer can be composed of a nematic liquid crystal aligned
substantially perpendicularly to substrates and having a negative
dielectric anisotropy. A first retardation film having an optically
negative uniaxiality, a second retardation film having an optically
positive uniaxiality, and a first polarizer are arranged in that
order outside an upper substrate, and a third retardation film
having an optically negative uniaxiality, a fourth retardation film
having an optically positive uniaxiality, a second polarizer, and
illumination means are arranged in that order outside a lower
substrate.
Inventors: |
Maeda, Tsuyoshi; (Ryuo-cho,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
32716069 |
Appl. No.: |
10/699539 |
Filed: |
November 3, 2003 |
Current U.S.
Class: |
349/119 |
Current CPC
Class: |
G02F 1/133567 20210101;
G02F 1/133562 20210101; G02F 1/133541 20210101; G02F 2413/14
20130101; G02F 1/1393 20130101; G02F 2413/13 20130101; G02F
1/133555 20130101; G02F 1/133634 20130101 |
Class at
Publication: |
349/119 |
International
Class: |
G02F 001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2002 |
JP |
2002-325238 |
Jul 29, 2003 |
JP |
2003-203099 |
Claims
What is claimed is:
1. A liquid crystal display device, comprising: a liquid crystal
layer that is held between a first substrate and a second
substrate, in which each of dots contains a reflective display
region for reflective display and a transmissive display region for
transmissive display, the liquid crystal layer being composed of a
nematic liquid crystal aligned substantially perpendicularly to the
substrates and having a negative dielectric anisotropy; a first
retardation film having an optically negative uniaxiality, a second
retardation film having an optically positive uniaxiality, and a
first polarizer that are arranged in that order outside the first
substrate; and a third retardation film having an optically
negative uniaxiality, a fourth retardation film having an optically
positive uniaxiality, a second polarizer, and an illumination
device that are arranged in that order outside the second
substrate.
2. A liquid crystal display device, comprising: a liquid crystal
layer that is held between a first substrate and a second
substrate, in which each of dots contains a reflective display
region for reflective display and a transmissive display region for
transmissivedisplay, the liquid crystal layer being composed of a
nematic liquid crystal aligned substantially perpendicularly to the
substrates and having a negative dielectric anisotropy; a first
retardation film having an optically negative uniaxiality, a second
retardation film having an optically positive uniaxiality, and a
first polarizer that are arranged in that order outside the first
substrate; and a fourth retardation film having an optically
positive uniaxiality, a second polarizer, and an illumination
device-that are arranged in that order outside the second
substrate.
3. A liquid crystal display device, comprising: a liquid crystal
layer that is held between a first substrate and a second
substrate, in which each of dots contains a reflective display
region for reflective display and a transmissive display region for
transmissivedisplay, the liquid crystal layer being composed of a
nematic liquid crystal aligned substantially perpendicularly to the
substrates and having a negative dielectric anisotropy; a second
retardation film having an optically positive uniaxiality, and a
first polarizer that are arranged in that order outside the first
substrate; and a third retardation film having an optically
negative uniaxiality, a fourth retardation film having an optically
positive uniaxiality, a second polarizer, and an illumination
device that are arranged in that order outside the second
substrate.
4. A liquid crystal display device according to claim 1, the
thickness of the liquid crystal layer being smaller in the
reflective display region than in the transmissive display
region.
5. A liquid crystal display device according to claim 1, wherein,
when nz1 and nz3 represent the refractive indices of the first
retardation film and the third retardation film in a Z-axis
direction serving as a thickness direction, nx1 and nx3 represent
the refractive indices thereof in an X-axis direction serving as
one direction in a plane perpendicular to the Z-axis direction, ny1
and ny3 represent the refractive indices thereof in a Y-axis
direction perpendicular to the Z-axis and X-axis directions, and d1
and d3 represent a thicknesses thereof in the Z-axis direction,
nx1.apprxeq.ny1>nz1 and nx3.apprxeq.ny3>nz3; and wherein a
sum W1 of the retardation (nx1-nz1).times.d1 of the first
retardation film and the retardation (nx3-nz3).times.d3 of the
third retardation film has the following relationship with a
retardation Rt of the liquid crystal layer in the transmissive
display region: 0.5.times.Rt.ltoreq.W1.- ltoreq.0.75.times.Rt.
6. A liquid crystal display device according to claim 1, wherein,
when nz1 and nz3 represent refractive indices of the first
retardation film and the third retardation film in a Z-axis
direction serving as a thickness direction, nx1 and nx3 represent
the refractive indices thereof in an X-axis direction serving as
one direction in a plane perpendicular to the Z-axis, ny1 and ny3
represent the refractive indices thereof in a direction of a Y-axis
perpendicular to the Z-axis and X-axis directions, and d1 and d3
represent a thicknesses thereof in the Z-axis direction,
nx1.apprxeq.ny1>nz1 and nx3.apprxeq.ny3>nz3; wherein, when
nz2 and nz4 represent refractive indices of the second retardation
film and the fourth retardation film in the Z-axis direction
serving as the thickness direction, nx2 and nx4 represent a
refractive indices thereof in the X-axis direction serving as one
direction in a plane perpendicular to the Z-axis, ny2 and ny4
represent refractive indices thereof in the Y-axis direction
perpendicular to the Z-axis and X-axis directions, and d2 and d4
represent the thicknesses thereof in the Z-axis direction,
nx2>ny2.apprxeq.nz2 and nx4>ny4.apprxeq.nz4; and wherein a
sum W1 of the retardation (nx1-nz1).times.d1 of the first
retardation film, the retardation (nx3-nz3).times.d3 of the third
retardation film, the retardation ((nx2+ny2)/2-nz2).times.d2 of the
second retardation film in the XY plane and in the Z-axis
direction, and the retardation ((nx4+ny4)/2-nz4).times.d4 of the
fourth retardation film in the XY plane and in the Z-axis direction
has the following relationship with a retardation Rt of the liquid
crystal layer in the transmissive display region:
0.5.times.Rt.ltoreq.W1.ltoreq.0.75.times.Rt.
7. A liquid crystal display device according to claim 2, wherein,
when nz1 represents a refractive index of the first retardation
film in Z-axis direction serving as a thickness direction, nx1
represents the refractive index thereof in an X-axis direction
serving as one direction in a plane perpendicular to the Z-axis,
ny1 represents the refractive index thereof in the Y-axis direction
perpendicular to the Z-axis and X-axis directions, and d1
represents a thickness thereof in the Z-axis direction,
nx1.apprxeq.ny1>nz1; and wherein the retardation
(nx1-nz1).times.d1 of the first retardation film has the following
relationship with a retardation Rt of the liquid crystal layer in
the transmissive display region:
0.5.times.Rt.ltoreq.(nx1-nz1).times.d1.ltore- q.0.75.times.Rt.
8. A liquid crystal display device according to claim 2, wherein,
when nz1 represents a refractive index of the first retardation
film in a Z-axis direction serving as a thickness direction, nx1
represents the refractive index thereof in an X-axis direction
serving as one direction in a plane perpendicular to the Z-axis,
ny1 represents the refractive index thereof in the Y-axis direction
perpendicular to the Z-axis and X-axis directions, and d1
represents a thickness thereof in the Z-axis direction,
nx1.apprxeq.ny1>nz1; wherein, when nz2 and nz4 represent
refractive indices of the second retardation film and the fourth
retardation film in the Z-axis direction serving as the thickness
direction, nx2 and nx4 represent the refractive indices thereof in
the X-axis direction serving as one direction in a plane
perpendicular to the Z-axis direction, ny2 and ny4 represent the
refractive indices thereof in the Y-axis direction perpendicular to
the Z-axis and X-axis directions, and d2 and d4 represent the
thicknesses thereof in the Z-axis direction, nx2>ny2.apprxeq.nz2
and nx4>ny4.apprxeq.nz4; and wherein a sum W2 of the retardation
(nx1-nz1).times.d1 of the first retardation film, the retardation
((nx2+ny2)/2-nz2).times.d2 of the second retardation film in the XY
plane and in the Z-axis direction, and the retardation
((nx4+ny4)/2-nz4).times.d4 of the fourth retardation film in the XY
plane and in the Z-axis direction has the following relationship
with a retardation Rt of the liquid crystal layer in the
transmissive display region:
0.5.times.Rt.ltoreq.W2.ltoreq.0.75.times.Rt.
9. A liquid crystal display device according to claim 3, wherein,
when nz3 represents a refractive index of the third retardation
film in a Z-axis direction serving as the thickness direction, nx3
represents a refractive index thereof in an X-axis direction
serving as one direction in a plane perpendicular to the Z-axis
direction, ny3 represents the refractive index thereof in the
Y-axis direction perpendicular to the Z-axis and X-axis directions,
and d3 represents the thickness thereof in the Z-axis direction,
nx3.apprxeq.ny3>nz3; and wherein retardation (nx3-nz3).times.d3
of the third retardation film has the following relationship with a
retardation Rt of the liquid crystal layer in the transmissive
display region: 0.5.times.Rt.ltoreq.(nx3-nz3).times.d3.ltore-
q.0.75.times.Rt.
10. A liquid crystal display device according to claim 3, wherein,
when nz3 represents the refractive index of the third retardation
film in a Z-axis direction serving as a thickness direction, nx3
represents the refractive index thereof in an X-axis direction
serving as one direction in a plane perpendicular to the Z-axis
direction, ny3 represents a refractive index thereof in a Y-axis
direction perpendicular to the Z-axis and X-axis directions, and d3
represents a thickness thereof in the Z-axis direction,
nx3.apprxeq.ny3>nz3; wherein, when nz2 and nz4 represent
refractive indices of the second retardation film and the fourth
retardation film in the Z-axis direction serving as the thickness
direction, nx2 and nx4 represent refractive indices thereof in the
X-axis direction serving as one direction in a plane perpendicular
to the Z-axis direction, ny2 and ny4 represent refractive indices
thereof in the Y-axis direction perpendicular to the Z-axis and
X-axis directions, and d2 and d4 represent the thicknesses thereof
in the Z-axis direction, nx2>ny2.apprxeq.nz2 and
nx4>ny4.apprxeq.nz4; and wherein a sum W3 of the retardation
(nx1-nz1 ).times.d1 of the first retardation film, the retardation
(nx3-nz3).times.d3 of the third retardation film, the retardation
((nx2+ny2)/2-nz2).times.d2 of the second retardation film in the XY
plane and in the Z-axis direction, and the retardation
((nx4+ny4)/2-nz4).times.d4 of the fourth retardation film in the XY
plane and in the Z-axis direction has the following relationship
with a retardation Rt of the liquid crystal layer in the
transmissive display region:
0.5.times.Rt.ltoreq.W3.ltoreq.0.75.times.Rt.
11. A liquid crystal display device according to claim 1, wherein,
when nx2 and nx4 represent refractive indices of the second
retardation film and the fourth retardation film in the X-axis
direction serving as one direction in a plane perpendicular to the
Z-axis direction serving as the thickness direction, ny2 and ny4
represent a refractive indices thereof in the Y-axis direction
perpendicular to the Z-axis and X-axis directions, and d2 and d4
represent thicknesses thereof in the Z-axis direction, the X-axis
of the second retardation film and the X-axis of the fourth
retardation film are orthogonal to each other, and the following
condition is satisfied: (nx2-ny2).times.d2=(nx4-ny4).times.d4.
12. A liquid crystal display device according to claim 11, the
second retardation film and the fourth retardation film satisfying
the following condition: 100
nm.ltoreq.(nx2-ny2).times.d2=(nx4-ny4).times.d4.ltoreq.160 nm.
13. A liquid crystal display device according to claim 1, the
second retardation film being composed of two or more oriented
films that convert linearly polarized light incident from the first
polarizer into circularly polarized light in a broad band, and the
fourth retardation film being composed of two or more oriented
films that convert linearly polarized light incident from the
second polarizer into circularly polarized light in a broad
band.
14. A liquid crystal display device according to claim 1, the
second retardation film being composed of two or more oriented
films that convert linearly polarized light incident from the first
polarizer into circularly polarized light in a broad band.
15. A liquid crystal display device according to claim 1, the
fourth retardation film being composed of two or more oriented
films that convert linearly polarized light incident from the
second polarizer into circularly polarized light in a broad
band.
16. A liquid crystal display device according to claim 1, the ratio
R(450)/R(590) of an in-plane retardation R(450) for 450 nm and an
in-plane retardation R(590) for 590 nm being less than 1 in the
second retardation film and the fourth retardation film.
17. A liquid crystal display device according to claim 1, the
polarization axis of the first polarizer and the polarization axis
of the second polarizer being orthogonal to each other.
18. A liquid crystal display device according to claim 1, the
retardation (nx1-nz1).times.d1 of the first retardation film being
substantially equal to the retardation (nx3-nz3).times.d3 of the
third retardation film.
19. A liquid crystal display device according to claim 1, wherein,
when nz1 represents the refractive index of the first retardation
film in a Z-axis direction serving as a thickness direction, nx1
represents the refractive index thereof in an X-axis direction
serving as one direction in a plane perpendicular to the Z-axis
direction, ny1 represents a refractive index thereof in a Y-axis
direction perpendicular to the Z-axis and X-axis directions, and d1
represents a thickness thereof in the Z-axis direction,
nx1.apprxeq.ny1>nz1; and wherein the retardation
(nx1-nz1).times.d1 of the first retardation film has the following
relationship with a retardation Rr of the liquid crystal layer in
the reflective display region:
0.5.times.Rr.ltoreq.(nx1-nz1).times.d1.ltoreq.- 0.75.times.Rr.
20. A liquid crystal display device according to claim 1, wherein,
when nz1 represents a refractive index of the first retardation
film in a Z-axis direction serving as a thickness direction, nx1
represents a refractive index thereof in an X-axis direction
serving as one direction in a plane perpendicular to the Z-axis
direction, ny1 represents a refractive index thereof in a Y-axis
direction perpendicular to the Z-axis and X-axis directions, and d1
represents a thickness thereof in the Z-axis direction,
nx1.apprxeq.ny1>nz1; wherein, when nz2 represents a refractive
index of the second retardation film in the Z-axis direction
serving as the thickness direction, nx2 represents the refractive
index thereof in the X-axis direction serving as one direction in a
plane perpendicular to the Z-axis direction, ny2 represents the
refractive index thereof in the Y-axis direction perpendicular to
the Z-axis and X-axis directions, and d2 represents the thickness
thereof in the Z-axis direction, nx2>ny2.apprxeq.nz2; and
wherein a sum W4 of the retardation (nx1-nz1).times.d1 of the first
retardation film, and the retardation ((nx2+ny2)/2-nz2).times.d2 of
the second retardation film in the XY plane and in the Z-axis
direction has the following relationship with a retardation Rr of
the liquid crystal layer in the reflective display region:
0.5.times.Rr.ltoreq.W4.ltoreq.0.75.times.Rr.
21. A liquid crystal display device according to claim 1, a
reflective layer being provided in the reflective display region to
reflect incident light.
22. A liquid crystal display device according to claim 21, the
reflective layer being uneven to scatter and reflect incident
light.
23. A liquid crystal display device according to claim 1, the
X-axis directions of the second retardation film and the fourth
retardation film being orthogonal to each other, and the X-axis
directions of the second retardation film and the fourth
retardation film form an angle of approximately 45.degree.,
respectively, with the polarization axis of the first polarizer and
the polarization axis of the second polarizer.
24. A liquid crystal display device according to claim 1, an
electrode having an aperture being provided on an inner surface,
adjacent to the liquid crystal layer, of at least one of the first
substrate and the second substrate so as to drive the liquid
crystal.
25. A liquid crystal display device according to claim 1,
projections being provided on an electrode disposed on an inner
surface of at least one of the first substrate and the second
substrate adjacent to the liquid crystal layer.
26. A liquid crystal display device according to claim 24, one dot
containing at least two directors of the liquid crystal when the
liquid crystal is driven by the electrode.
27. An electronic device comprising the liquid crystal display
device according to claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a liquid crystal display
device and an electronic device. More particularly, the present
invention relates to a technique for achieving high-contrast
reflective and transmissive displays with a wide viewing angle in a
transflective liquid crystal display device having reflective and
transmissive structures.
[0003] 2. Description of Related Art
[0004] Transflective liquid crystal display devices that adopt
reflective and transmissive display modes can perform clear display
with reduced power consumption even in a dark environment by
switching between the reflective and transmissive display modes
according to ambient brightness. As such a transflective liquid
crystal display device, a liquid crystal display device has been
proposed in which a liquid crystal layer is held between
transmissive upper and lower substrates, a reflective film made of
metal, such as aluminum, and having a light-transmitting aperture
is provided on the inner side of the lower substrate, and the
reflective film functions as a transflective film. In this case, in
a reflective mode, external light incident from the upper substrate
passes through the liquid crystal layer, is reflected by the
reflective film disposed on the inner side of the lower substrate,
passes through the liquid crystal layer again, and is emitted from
the upper substrate for display. In a transmissive mode, light of a
backlight incident from the lower substrate passes through the
liquid crystal layer from the aperture of the reflective film, and
is directed to the outside from the upper substrate for display.
Therefore, a region of the reflective film where the aperture is
formed serves as a transmissive display region, and a region of the
reflective film where the aperture is not formed serves as a
reflective display region. Such a display device is described, for
example, in Japanese Unexamined Patent Application Publication No.
11-242226 (page 61, FIG. 1).
[0005] As another known art, a homeotropic liquid crystal display
device has been proposed which improves the viewing-angle
characteristic of liquid crystal, for example, in Japanese
Unexamined Patent Application Publication No. 5-113561 (page 5,
FIG. 1) see Patent 2).
SUMMARY OF THE INVENTION
[0006] In a known transflective liquid crystal display device that
adopts reflective and transmissive display modes, the viewing angle
is narrow in reflective and transmissive displays. In reflective
display, a polarizer and a retardation film on the viewer side
(upper side of the transflective liquid crystal device), and a
liquid crystal layer in a reflective display region through which
incident light passes twice must be designed. In transmissive
display, a polarizer and a retardation film on the viewer side
(upper side of the transflective liquid crystal device), a
polarizer and a retardation film on the side of an illumination
means (lower side of the transflective liquid crystal display
device), and a liquid crystal layer in a transmissive display
region through which incident from the illumination means passes
once must be designed. For this reason, it is quite difficult to
design high-contrast reflective and transmissive displays with a
wide viewing angle.
[0007] In an electronic device equipped with the known
transflective liquid crystal display device, the viewing angle is
narrow, and a range in which display is visible is limited.
Accordingly, an object of the present invention is to achieve
high-contrast reflective display and transmissive display with a
wide viewing angle in a transflective liquid crystal display device
having reflective and transmissive structures. Another object of
the present invention is to provide an electronic device equipped
with a highly visible display device.
[0008] In order to overcome the above problems, the present
invention can provide a liquid crystal display device including a
liquid crystal layer held between a first substrate and a second
substrate, in which each of dots contains a reflective display
region for reflective display and a transmissive display region for
transmissivedisplay. The liquid crystal layer is composed of a
nematic liquid crystal aligned substantially perpendicularly to the
substrates and having a negative dielectric anistropy. The device
can further include a first retardation film having an optically
negative uniaxiality, a second retardation film having an optically
positive uniaxiality, and a first polarizer are arranged in that
order outside the first substrate; and a third retardation film
having an optically negative uniaxiality, a fourth retardation film
having an optically positive uniaxiality, a second polarizer, and
an illumination device are arranged in that order outside the
second substrate.
[0009] In the above configuration, a high-contrast reflective
display can be achieved by the first polarizer, the second
retardation film having an optically positive uniaxiality, and the
vertically aligned liquid crystal layer, and a high-contrast
transmissive display can be achieved by the first polarizer, the
second retardation film having an optically positive uniaxiality,
the vertically aligned liquid crystal layer, the fourth retardation
film having an optically positive uniaxiality, and the second
polarizer. Furthermore, by interposing the first retardation film
having an optically negative uniaxiality between the second
retardation film having an optically positive uniaxiality and the
liquid crystal layer, the viewing-angle characteristic of the
vertically aligned liquid crystal layer when viewed from the
oblique direction can be compensated for, and reflective display
with a wide viewing angle can be achieved. By interposing the first
retardation film having an optically negative uniaxiality between
the second retardation film having an optically positive
uniaxiality and the liquid crystal layer, and interposing the third
retardation film having an optically negative uniaxiality between
the fourth retardation film having an optically positive
uniaxiality and the liquid crystal layer, the viewing-angle
characteristic of the vertically aligned liquid crystal layer when
viewed from the oblique direction can be compensated for, and
transmissive display with a wide viewing angle can be achieved.
[0010] The present invention also provides a liquid crystal display
device including a liquid crystal layer held between a first
substrate and a second substrate, in which each of dots contains a
reflective display region for reflective display and a transmissive
display region for transmissivedisplay. The liquid crystal layer
can be composed of a nematic liquid crystal aligned substantially
perpendicularly to the substrates and having a negative dielectric
anisotropy. The device can further include a first retardation film
having an optically negative uniaxiality, a second retardation film
having an optically positive uniaxiality, and a first polarizer are
arranged in that order outside the first substrate, and a fourth
retardation film having an optically positive uniaxiality, a second
polarizer, and illumination means are arranged in that order
outside the second substrate.
[0011] In the above configuration, a high-contrast reflective
display can be achieved by the first polarizer, the second
retardation film having an optically positive uniaxiality, and the
vertically aligned liquid crystal layer, and a high-contrast
transmissive display can be achieved by the first polarizer, the
second retardation film having an optically positive uniaxiality,
the vertically aligned liquid crystal layer, the fourth retardation
film having an optically positive uniaxiality, and the second
polarizer. Furthermore, by interposing the first retardation film
having an optically negative uniaxiality between the second
retardation film having an optically positive uniaxiality and the
liquid crystal layer, the viewing-angle characteristic of the
vertically aligned liquid crystal layer when viewed from the
oblique direction can be compensated for, and reflective display
with a wide viewing angle can be achieved. By interposing the first
retardation film having an optically negative uniaxiality between
the second retardation film having an optically positive
uniaxiality and the liquid crystal layer, the viewing-angle
characteristic of the vertically aligned liquid crystal layer when
viewed from the oblique direction can be compensated for, and
transmissive display with a wide viewing angle can be achieved.
[0012] The present invention can also provide a liquid crystal
display device including a liquid crystal layer held between a
first substrate and a second substrate, in which each of dots
contains a reflective display region for reflective display and a
transmissive display region for transmissive display. The liquid
crystal layer can be composed of a nematic liquid crystal aligned
substantially perpendicularly to the substrates and having a
negative dielectricanisotropy. The device can further include a
second retardation film having an optically positive uniaxiality,
and a first polarizer are arranged in that order outside the
firstsubstrate, and a third retardation film having an optically
negative uniaxiality, a fourth retardation film having an optically
positive uniaxiality, a second polarizer, and an illumination
device are arranged in that order outside the second substrate.
[0013] In the above configuration, a high-contrast reflective
display can be achieved by the first polarizer, the second
retardation film having an optically positive uniaxiality, and the
vertically aligned liquid crystal layer, and a high-contrast
transmissive display can be achieved by the first polarizer, the
second retardation film having an optically positive uniaxiality,
the vertically aligned liquid crystal layer, the fourth retardation
film having an optically positive uniaxiality, and the second
polarizer. Furthermore, by interposing the third retardation film
having an optically negative uniaxiality between the fourth
retardation film having an optically positive uniaxiality and the
liquid crystal layer, the viewing-angle characteristic of the
vertically aligned liquid crystal layer when viewed from the
oblique direction can be compensated for, and transmissive display
with a wide viewing angle can be achieved.
[0014] In the liquid crystal display device of the present
invention, the thickness of the liquid crystal layer can be smaller
in the reflective display region than in the transmissive display
region. This can achieve bright and high-contrast reflective and
transmissive displays. In the transflective liquid crystal display
device, for example, when d represents the thickness of the liquid
crystal layer, .DELTA.n represents the refractive index anisotropy
of liquid crystal, and .DELTA.nd represents the retardation of the
liquid crystal expressed by the product of the thickness and the
refractive index anisotropy, the retardation And of the liquid
crystal in the reflective display region is expressed by
2.times..DELTA.nd because incident light reaches the viewer after
passing through the liquid crystal layer twice. The retardation And
of the liquid crystal in the transmissive display region is
expressed by 1.times..DELTA.nd because light from the illumination
device (backlight) passes through the liquid crystal layer only
once. Since .DELTA.nd can be optimized in both the reflective and
transmissive display regions by setting the thickness of the liquid
crystal layer smaller in the reflective display region than in the
transmissive display region, bright and high-contrast reflective
display and transmissive display can be achieved.
[0015] In the liquid crystal display device of the present
invention, when nz1 and nz3 represent the refractive indices of the
first retardation film and the third retardation film in the Z-axis
direction serving as the thickness direction, nx1 and nx3 represent
the refractive indices thereof in the X-axis direction serving as
one direction in a plane perpendicular to the Z-axis direction, ny1
and ny3 represent the refractive indices thereof in the Y-axis
direction perpendicular to the Z-axis and X-axis directions, and d1
and d3 represent the thicknesses thereof in the Z-axis direction,
nx1.apprxeq.ny1>nz1 and nx3.apprxeq.ny3>nz3. The sum W1 of
the retardation (nx1-nz1).times.d1 of the first retardation film
and the retardation (nx3-nz3).times.d3 of the third retardation
film has the following relationship with the retardation Rt of the
liquid crystal layer in the transmissive display region:
0.5.times.Rt.ltoreq.W1.ltoreq.0.75.times.Rt.
[0016] In the liquid crystal display device of the present
invention, when nz1 and nz3 represent the refractive indices of the
first retardation film and the third retardation film in the Z-axis
direction serving as the thickness direction, nx1 and nx3 represent
the refractive indices thereof in the X-axis direction serving as
one direction in a plane perpendicular to the Z-axis direction, ny1
and ny3 represent the refractive indices thereof in the Y-axis
direction perpendicular to the Z-axis and X-axis directions, and d1
and d3 represent the thicknesses thereof in the Z-axis direction,
nx1.apprxeq.ny1>nz1 and nx3.apprxeq.ny3>nz3. When nz2 and nz4
represent the refractive indices of the second retardation film and
the fourth retardation film in the Z-axis direction serving as the
thickness direction, nx2 and nx4 represent the refractive indices
thereof in the X-axis direction serving as one direction in a plane
perpendicular to the Z-axis direction, ny2 and ny4 represent the
refractive indices thereof in the Y-axis direction perpendicular to
the Z-axis and X-axis directions, and d2 and d4 represent the
thicknesses thereof in the Z-axis direction, nx2>ny2.apprxeq.nz2
and nx4>ny4.apprxeq.nz4. The sum W1 of the retardation
(nx1-nz1).times.d1 of the first retardation film, the retardation
(nx3-nz3).times.d3 of the third retardation film, the retardation
((nx2+ny2)/2-nz2).times.d2 of the second retardation film in the XY
plane and in the Z-axis direction, and the retardation
((nx4+ny4)/2-nz4).times.d4 of the fourth retardation film in the XY
plane and in the Z-axis direction has the following relationship
with the retardation Rt of the liquid crystal layer in the
transmissive display region:
0.5.times.Rt.ltoreq.W1.ltoreq.0.75.times.Rt.
[0017] In this case, the viewing-angle characteristic of the
vertically aligned liquid crystal layer when viewed from the
oblique direction can be compensated for, and transmissive display
with a wide viewing angle can be achieved. By setting the
retardation (nx1-nz1).times.d1 of the first retardation film and
the retardation (nx3-nz3).times.d3 of the third retardation film
within the ranges of the present invention, the viewing-angle
characteristic of the vertically aligned liquid crystal layer in
the transmissive display region can be optically compensated for.
Furthermore, by adding the retardation ((nx2+ny2)/2-nz2).times.d2
of the second retardation film in the XY plane and in the Z-axis
direction, and the retardation ((nx4+ny4)/2-nz4).times.d4 of the
fourth retardation film in the XY plane and in the Z-axis direction
into the ranges of the present invention, the viewing-angle
characteristic of the vertically aligned liquid crystal layer in
the transmissive display region can be optically compensated for.
The first retardation film and the third retardation film may be
composed of a plurality of optically negative uniaxial films. The
retardation Rt of the liquid crystal layer is expressed by the
product .DELTA.n.times.d of the refractive index anisotropy
.DELTA.n of the liquid crystal and the thickness d of the liquid
crystal layer.
[0018] In the liquid crystal display device of the present
invention, when nz1 represents the refractive index of the first
retardation film in the Z-axis direction serving as the thickness
direction, nx1 represents the refractive index thereof in the
X-axis direction serving as one direction in a plane perpendicular
to the Z-axis direction, ny1 represents the refractive index
thereof in the Y-axis direction perpendicular to the Z-axis and
X-axis directions, and d1 represents the thickness thereof in the
Z-axis, nx1.apprxeq.ny1>nz1. The retardation (nx1-nz1).times.d1
of the first retardation film has the following relationship with
the retardation Rt of the liquid crystal layer in the transmissive
display region:
0.5.times.Rt.ltoreq.(nx1-nz1).times.d1.ltoreq.0.75.times.Rt.
[0019] In the liquid crystal display device of the present
invention, when nz1 represents the refractive index of the first
retardation film in the Z-axis direction serving as the thickness
direction, nx1 represents the refractive index thereof in the
X-axis direction serving as one direction in a plane perpendicular
to the Z-axis direction, ny1 represents the refractive index
thereof in the Y-axis direction perpendicular to the Z-axis and
X-axis directions, and d1 represents the thickness thereof in the
Z-axis direction, nx1.apprxeq.ny1>nz1. When nz2 and nz4
represent the refractive indices of the second retardation film and
the fourth retardation film in the Z-axis direction serving as the
thickness direction, nx2 and nx4 represent the refractive indices
thereof in the X-axis direction serving as one direction in a plane
perpendicular to the Z-axis direction, ny2 and ny4 represent the
refractive indices thereof in the Y-axis direction perpendicular to
the Z-axis and X-axis directions, and d2 and d4 represent the
thicknesses thereof in the Z-axis direction, nx2>ny2.apprxeq.nz2
and nx4>ny4.apprxeq.nz4. The sum W2 of the retardation
(nx1-nz1).times.d1 of the first retardation film, the retardation
((nx2+ny2)/2-nz2).times.d2 of the second retardation film in the XY
plane and in the Z-axis direction, and the retardation
((nx4+ny4)/2-nz4).times.d4 of the fourth retardation film in the XY
plane and in the Z-axis direction has the following relationship
with the retardation Rt of the liquid crystal layer in the
transmissive display region:
0.5.times.Rt.ltoreq.W2.ltoreq.0.75.times.Rt.
[0020] In this case, the viewing-angle characteristic of the
vertically aligned liquid crystal layer when viewed from the
oblique direction can be compensated for, and transmissive display
with a wide viewing angle can be achieved. By setting the
retardation (nx1-nz1).times.d1 of the first retardation film within
the range of the present invention, the viewing-angle
characteristic of the vertically aligned liquid crystal layer in
the transmissive display region can be optically compensated for.
Furthermore, by setting the retardation ((nx2+ny2)/2-nz2).times.d2
of the second retardation film in the XY plane and in the Z-axis
direction, and the retardation ((nx4+ny4)/2-nz4).times.d4 of the
fourth retardation film in the XY plane and in the Z-axis direction
within the ranges of the present invention, the viewing-angle
characteristic of the vertically aligned liquid crystal layer in
the transmissive display region can be optically compensated for.
The first retardation film may be composed of a plurality of
optically negative uniaxial films.
[0021] In the liquid crystal display device of the present
invention, when nz3 represents the refractive index of the third
retardation film in the Z-axis direction serving as the thickness
direction, nx3 represents the refractive index thereof in the
X-axis direction serving as one direction in a plane perpendicular
to the Z-axis direction, ny3 represents the refractive index
thereof in the Y-axis direction perpendicular to the Z-axis and
X-axis directions, and d3 represents the thickness thereof in the
Z-axis direction, nx3.apprxeq.ny3>nz3. The retardation
(nx3-nz3).times.d3 of the third retardation film has the following
relationship with the retardation Rt of the liquid crystal layer in
the transmissive display region:
0.5.times.Rt.ltoreq.(nx3-nz3).times.d3.ltoreq.0.75.times.Rt.
[0022] In the liquid crystal display device of the present
invention, when nz3 represents the refractive index of the third
retardation film in the Z-axis direction serving as the thickness
direction, nx3 represents the refractive index thereof in the
X-axis direction serving as one direction in a plane perpendicular
to the Z-axis direction, ny3 represents the refractive index
thereof in the Y-axis direction perpendicular to the Z-axis and
X-axis directions, and d3 represents the thickness thereof in the
Z-axis direction, nx3.apprxeq.ny3>nz3. When nz2 and nz4
represent the refractive indices of the second retardation film and
the fourth retardation film in the Z-axis direction serving as the
thickness direction, nx2 and nx4 represent the refractive indices
thereof in the X-axis direction serving as one direction in a plane
perpendicular to the Z-axis direction, ny2 and ny4 represent the
refractive indices thereof in the Y-axis direction perpendicular to
the Z-axis and X-axis directions, and d2 and d4 represent the
thicknesses thereof in the Z-axis direction, nx2>ny2.apprxeq.nz2
and nx4>ny4.apprxeq.nz4. The sum W3 of the retardation
(nx1-nz1).times.d1 of the first retardation film, the retardation
(nx3-nz3).times.d3 of the third retardation film, the retardation
((nx2+ny2)/2-nz2).times.d2 of the second retardation film in the XY
plane and in the Z-axis direction, and the retardation
((nx4+ny4)/2-nz4).times.d4 of the fourth retardation film in the XY
plane and in the Z-axis direction has the following relationship
with the retardation Rt of the liquid crystal layer in the
transmissive display region:
0.5.times.Rt.ltoreq.W3.ltoreq.0.75.times.Rt.
[0023] In this case, the viewing-angle characteristic of the
vertically aligned liquid crystal layer when viewed from the
oblique direction can be compensated for, and transmissive display
with a wide viewing angle can be achieved. By setting the
retardation (nx3-nz3).times.d3 of the third retardation film within
the range of the present invention, the viewing-angle
characteristic of the vertically aligned liquid crystal layer in
the transmissive display region can be optically compensated for.
Furthermore, by adding the retardation ((nx2+ny2)/2-nz2).times.d2
of the second retardation film in the XY plane and in the Z-axis
direction, and the retardation ((nx4+ny4)/2-nz4).times.d4 of the
fourth retardation film in the XY plane and in the Z-axis direction
into the ranges of the present invention, the viewing-angle
characteristic of the vertically aligned liquid crystal layer in
the transmissive display region can be optically compensated for.
The third retardation film may be composed of a plurality of
optically negative uniaxial films.
[0024] In the liquid crystal display device of the present
invention, when nx2 and nx4 represent the refractive indices of the
second retardation film and the fourth retardation film in the
X-axis direction serving as one direction in a plane perpendicular
to the thickness direction (Z-axis), ny2 and ny4 (nx2>ny2 and
nx4>ny4) represent the refractive indices thereof in the Y-axis
direction perpendicular to the Z-axis and X-axis directions, and d2
and d4 represent the thicknesses thereof in the Z-axis direction,
the X-axis of the second retardation film and the X-axis of the
fourth retardation film are orthogonal to each other, and the
following condition is satisfied:
(nx2-ny2).times.d2=(nx4-ny4).times.d4.
[0025] In this case, the retardations of the second and fourth
retardation films in the panel surface (XY plane) of the liquid
crystal display device can be cancelled each other, and it is
possible to achieve the best possible black display (in the case
that the polarization axis of the first polarizer and the
polarization axis of the second polarizer are orthogonal) and the
best possible white display (in the case that the polarization axis
of the first polarizer and the polarization axis of the second
polarizer are parallel) with the first polarizer and the second
polarizer.
[0026] In the liquid crystal display device of the present
invention, the second retardation film and the fourth retardation
film satisfy the following condition:
100 nm.ltoreq.(nx2-ny2).times.d2=(nx4-ny4).times.d4.ltoreq.160
nm
[0027] In this case, the first polarizer and the second retardation
film can produce circularly or elliptically polarized light with
small wavelength dispersion, and the second polarizer and the
fourth retardation film can produce circularly or elliptically
polarized light with small wavelength dispersion. This makes it
possible to switch the liquid crystal display device by using
circularly or elliptically polarized light, and to achieve
high-contrast reflective display and transmissive display.
[0028] In the liquid crystal display device of the present
invention, the second retardation film can be composed of two or
more oriented films for converting linearly polarized light
incident from the first polarizer into circularly polarized light
in a broad band, and the fourth retardation film is composed of two
or more oriented films for converting linearly polarized light
incident from the second polarizer into circularly polarized light
in a broad band. In this case, since light with almost all the
wavelengths in the visible region can be converted into ideal
circularly polarized light, it is possible to achieve high-contrast
reflective display and transmissive display without producing
unnecessary color. For example, a broadband circularly polarization
plate can be obtained by stacking a half-wave plate and a
quarter-wave plate at an appropriate angle (formed by the direction
of orientation).
[0029] In the liquid crystal display device of the present
invention, the second retardation film can be composed of two or
more oriented films for converting linearly polarized light
incident from the first polarizer into circularly polarized light
in a broad band. In this case, since light with almost all the
wavelengths in the visible region can be converted into ideal
circularly polarized light, it is possible to achieve high-contrast
reflective display without producing unnecessary color. For
example, a broadband circularly polarization plate can be obtained
by stacking a half-wave plate and a quarter-wave plate at an
appropriate angle (formed by the direction of orientation).
[0030] In the liquid crystal display device of the present
invention, the fourth retardation film can be composed of two or
more oriented films for converting linearly polarized light
incident from the second polarizer into circularly polarized light
in a broad band. In this case, since light with almost all the
wavelengths in the visible region can be converted into ideal
circularly polarized light, it is possible to achieve high-contrast
transmissive display without producing unnecessary color. For
example, a broadband circularly polarization plate can be obtained
by stacking a half-wave plate and a quarter-wave plate at an
appropriate angle (formed by the direction of orientation).
[0031] In the liquid crystal display device of the present
invention, in the second retardation film and the fourth
retardation film, the ratio R(450)/R(590) of an in-plane
retardation R(450) for 450 nm and an in-plane retardation R(590)
for 590 nm is less than 1. In this case, since broadband circularly
polarized light can be produced by the combination with the first
polarizer or the second polarizer, it is possible to achieve
high-contrast reflective display and transmissive display without
producing unnecessary color.
[0032] In the liquid crystal display device of the present
invention, the polarization axis of the first polarizer and the
polarization axis of the second polarizer can be orthogonal to each
other. In this case, the best possible black display can be
performed with the first polarizer and the second polarizer.
Therefore, a high-contrast transmissive display is possible.
[0033] In the liquid crystal display device of the present
invention, the retardation (nx1-nz1).times.d1 of the first
retardation film can be substantially equal to the retardation
(nx3-nz3).times.d3 of the third retardation film. In this case, the
viewing angle in the reflective display region in viewing the
liquid crystal layer from the oblique direction can be compensated
for by the first retardation film having an optically negative
uniaxiality, and the viewing angle in the transmissive display
region in viewing the liquid crystal layer from the oblique
direction can be compensated for by the first and third retardation
films having an optically negative uniaxiality. Since light passes
through the liquid crystal layer twice in the reflective display
region and passes therethrough only once in the transmissive
display region, the thickness of the liquid crystal layer in the
transmissive display region is substantially double the thickness
in the reflective display region. For this reason, it is necessary
to set the retardation of the first retardation film substantially
equal to the retardation of the third retardation film.
[0034] In the liquid crystal display device of the present
invention, when nz1 represents the refractive index of the first
retardation film in the Z-axis direction serving as the thickness
direction, nx1 represents the refractive index thereof in the
X-axis direction serving as one direction in a plane perpendicular
to the Z-axis direction, ny1 represents the refractive index
thereof in the Y-axis direction perpendicular to the Z-axis and
X-axis directions, and d1 represents the thickness thereof in the
Z-axis direction, nx1.apprxeq.ny1>nz1. The retardation
(nx1-nz1).times.d1 of the first retardation film has the following
relationship with the retardation Rr of the liquid crystal layer in
the reflective display region:
0.5.times.Rr.ltoreq.(nx1-nz1).times.d1.ltoreq.0.75.times.Rr
[0035] In the liquid crystal display device of the present
invention, when nz1 represents the refractive index of the first
retardation film in the Z-axis direction serving as the thickness
direction, nx 1 represents the refractive index thereof in the
X-axis direction serving as one direction in a plane perpendicular
to the Z-axis direction, ny1 represents the refractive index
thereof in the Y-axis direction perpendicular to the Z-axis and
X-axis directions, and d1 represents the thickness thereof in the
Z-axis direction, nx1.apprxeq.ny1>nz1. When nz2 represents the
refractive index of the second retardation film in the Z-axis
direction serving as the thickness direction, nx2 represents the
refractive index thereof in the X-axis direction serving as one
direction in a plane perpendicular to the Z-axis direction, ny2
represents the refractive index thereof in the Y-axis direction
perpendicular to the Z-axis and X-axis directions, and d2
represents the thickness thereof in the Z-axis direction,
nx2>ny2.apprxeq.nz2. The sum W4 of the retardation
(nx1-nz1).times.d1 of the first retardation film, and the
retardation ((nx2+ny2)/2-nz2).times.d2 of the second retardation
film in the XY plane and in the Z-axis direction has the following
relationship with the retardation Rr of the liquid crystal layer in
the reflective display region:
0.5.times.Rr.ltoreq.W4.ltoreq.0.75.times.Rr.
[0036] In this case, the viewing angle of the liquid crystal layer
in the reflective display region when viewed from the oblique
direction can be compensated for by the first retardation film
having an optically negative uniaxiality. By adding the second
retardation film having an optically positive uniaxiality, the
viewing angle of the liquid crystal layer in the reflective display
region when viewed from the oblique direction can be compensated
for.
[0037] In the liquid crystal display device of the present
invention, a reflective layer is provided in the reflective display
region to reflect incident light. Since external light can be
reflected by the reflective layer, reflective display is
possible.
[0038] In the liquid crystal display device of the present
invention, the reflective layer has irregularities to scatter and
reflect incident light. In this case, since incident light is
scattered and reflected by the reflective layer having
irregularities, reflective display can be viewed with a wide
viewing angle.
[0039] In the liquid crystal display device of the present
invention, the X-axis directions of the second retardation film and
the fourth retardation film can be orthogonal to each other, and
the X-axis directions of the second retardation film and the fourth
retardation film form an angle of approximately 45.degree.,
respectively, with the polarization axis of the first polarizer and
the polarization axis of the second polarizer.
[0040] In this case, the retardations of the second and fourth
retardation films in the panel surface (XY plane) of the liquid
crystal display device can be cancelled each other, and it is
possible to perform the best possible black display with the first
polarizer and the second polarizer. Moreover, the first polarizer
and the second retardation film, and the second polarizer and the
fourth retardation film can produce circularly polarized light.
This makes it possible to switch the liquid crystal display device
with circularly polarized light, and to achieve bright and
high-contrast reflective display and transmissive display.
[0041] In the liquid crystal display device of the present
invention, an electrode having an aperture can be provided on an
inner surface, adjacent to the liquid crystal layer, of at least
one of the first substrate and the second substrate so as to drive
the liquid crystal. In this case, since an oblique electric field
is produced in the liquid crystal layer by the aperture of the
electrode for driving the liquid crystal, a plurality of director
directions of liquid crystal molecules can be produced in one dot
during voltage application. This can achieve a transflective liquid
crystal display device with a wide viewing angle.
[0042] In the liquid crystal display device of the present
invention, projections can be provided on an electrode disposed on
an inner surface of at least one of the first substrate and the
second substrate adjacent to the liquid crystal layer. In this
case, since the tilting direction of liquid crystal molecules can
be controlled by the projections provided on the electrode, a
plurality of director directions of the liquid crystal molecules
can be produced in one dot during voltage application. This can
achieve a transflective liquid crystal display device with a wide
viewing angle.
[0043] In the liquid crystal display device of the present
invention, one dot contains at least two directors of the liquid
crystal when the liquid crystal is driven by the electrode. This
can achieve a transflective liquid crystal display device with a
wide viewing angle.
[0044] An electronic device of the present invention can include
the above-described transflective liquid crystal display device.
This can achieve an electronic device equipped with a highly
visible display device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The invention will be described with reference to the
accompanying drawings, wherein like numerals reference like
elements, and wherein:
[0046] FIG. 1 is a schematic view showing a partial cross-sectional
configuration of a liquid crystal display device according to a
first embodiment of the present invention;
[0047] FIG. 2 is a schematic view showing a partial cross-sectional
configuration of a liquid crystal display device according to a
second embodiment of the present invention;
[0048] FIG. 3 is a schematic view showing a partial cross-sectional
configuration of a liquid crystal display device according to a
third embodiment of the present invention;
[0049] FIG. 4 is a perspective view of an example of an electronic
device according to the present invention;
[0050] FIG. 5 is a perspective view of another example of an
electronic device according to the present invention;
[0051] FIG. 6 is a perspective view of a further example of an
electronic device according to the present invention;
[0052] FIG. 7 is a table showing the relationship between W1/Rt and
a transmissive-display viewing range in the liquid crystal display
device according to the first embodiment of the present
invention;
[0053] FIG. 8 is a table showing the relationship between W2/Rt and
a transmissive-display viewing range in the liquid crystal display
device according to the second embodiment of the present
invention;
[0054] FIG. 9 is a table showing the relationship between W3/Rt and
a transmissive-display viewing range in the liquid crystal display
device according to the third embodiment of the present
invention;
[0055] FIG. 10 is a table showing the relationship between W4/Rr
and a reflective-display viewing range in the liquid crystal
display device of the present invention;
[0056] FIG. 11 is a graph showing the relationship between the
luminance of a backlight and the polar angle; and
[0057] FIG. 12 is an explanatory view showing an action of
compensation for a viewing-angle characteristic.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0058] Embodiments of the present invention will be described below
with reference to the drawings.
[0059] FIG. 1 shows a first embodiment in which a configuration of
the present invention is applied to an active-matrix liquid crystal
display device. A liquid crystal display device of the first
embodiment has a basic configuration in which a liquid crystal
layer 110 is held between upper and lower substrates 105 and 113
opposing each other and made of a transparent glass or the like, as
shown by a cross-sectional configuration in FIG. 1. Although not
shown, a sealing material is, in actuality, disposed on the
peripheries of the substrates 105 and 13, and the liquid crystal
layer 110 is surrounded by the substrates 105 and 113 and the
sealing material to be sealed and held between the substrates 105
and 113. While a backlight including a light source, a light guide
plate, and so on is provided below the lower substrate 113, it is
not shown in FIG. 1.
[0060] Retardation films 104 and 103 and a polarizer 102 are
arranged on an upper side (viewer side) of the upper substrate 105,
and retardation films 114 and 115 and a polarizer 116 are arranged
on a lower side of the lower substrate 113. The polarizers 102 and
116 transmit only linearly polarized light polarized in one
direction, of external light incident from the upper side and light
of the backlight incident from the lower side, and the retardation
films 103 and 15 convert linearly polarized light transmitted
through the polarizers 102 and 116 into circularly polarized light
(including elliptically polarized light). Therefore, the polarizers
102 and 16 and the retardation films 103 and 115 function as
circularly-polarized-light introducing devices. In this embodiment,
one side on which the backlight is provided is designated as a
lower side, and the other side from which external light enters is
designated as an upper side. The substrate 105 and the substrate
113 are also referred, respectively, to an upper substrate and a
lower substrate.
[0061] A transparent electrode 106 made of ITO (Indium Tin Oxide)
or the like can be provided on a side of the upper substrate 105
adjacent to the liquid crystal layer 110, and a vertical alignment
film (not shown) is provided on a side of the transparent electrode
106 adjacent to the liquid crystal layer 110 so as to cover the
transparent electrode 106. A reflective electrode 108 also
functioning as a reflecting layer, and a transparent electrode 112
are provided on a side of the lower substrate 113 adjacent to the
liquid crystal layer 110. The reflective electrode 108 functions as
a reflective display region, and the transparent electrode 112
functions as a transmissive display region. The reflective
electrode 108 is made of a reflective, that is, high-reflectance
metal material, such as Al or Ag, and is shaped like a rectangular
frame in plan view. A vertical alignment film (not shown) is
provided on a side of the reflective electrode 108 adjacent to the
liquid crystal layer 110.
[0062] A liquid-crystal-layer thickness control layer 109 made of
resin, such as acrylic resin, enables the reflective electrode 108
to have an uneven shape, and makes the thickness of the liquid
crystal layer 110 smaller in the reflective display region than in
the transmissive display region. Such a structure can be formed by
a photolithographic process. While the reflecting layer in the
reflective display region also functions as a liquid-crystal
driving electrode, a liquid-crystal driving electrode may be
provided separately. By conducting a photolithographic process in
which a resist is applied on a glass substrate serving as the lower
substrate 113, etching is performed with fluorinated acid, and the
resist is stripped after etching, fine irregularities may be
formed, and a reflective layer may be formed thereon to obtain an
uneven reflective layer.
[0063] Dielectric projections 107 made of acrylic resin are
provided on the transparent electrode 106 on the inner side of the
upper substrate 105 so as to apply an oblique electric field, which
is not orthogonal to the surfaces of the substrates 105 and 113, to
the liquid crystal layer 110 in cooperation with an aperture 1111
of the transparent electrode 112 provided on the inner side of the
lower substrate 113. The dielectric projections 107 and the
aperture 111 of the transparent electrode 112 allow a plurality of
directors of the liquid crystal layer 110 to be produced in one dot
by applying a voltage to the electrodes 106, 108, and 112, and this
achieves a liquid crystal display device that does not depend on
the viewing angle.
[0064] Although not shown in FIG. 1, at the peripheral corner of
each dot, a thin-film transistor serving as a switching element for
driving the electrodes 108 and 112 can be provided and a gate line
and a source line are also provided to feed electricity to the
thin-film transistor. Instead of the thin-film transistor, a
two-terminal linear element or other switching elements may be
adopted as the switching element.
[0065] Operational advantages of the transflective liquid crystal
display device having the configuration shown in FIG. 1 will now be
described. In order to perform reflective display, light incident
from the outside of the device is used, and the incident light is
guided to the liquid crystal layer 110 through the polarizer 102,
the retardation films 103 and 104, the upper substrate 105, and the
electrode 106.
[0066] In the reflective display region, after the incident light
passes through the liquid crystal layer 110, it is reflected by the
reflective electrode 108. The reflected light passes again through
the liquid crystal layer 110, is returned to the outside of the
device through the electrode 106, the upper substrate 105, the
retardation films 104 and 103, and the polarizer 102, and reaches a
viewer to perform reflective display. In such reflective display,
the polarization state of the light passing through the liquid
crystal layer 110 is changed by controlling the alignment of liquid
crystal in the liquid crystal layer 110 by the electrodes 106 and
108, thereby producing light and dark displays.
[0067] In order to perform transmissive display, light emitted from
the backlight (illumination means) enters through the polarizer
116, the retardation films 115 and 114, and the substrate 113. In
this case, in the transmissive display region, the light incident
from the substrate 113 passes through the electrode 112, the liquid
crystal layer 110, the electrode 106, the substrate 105, the
retardation films 104 and 103, and the polarizer 102 in that order
in order to perform transmissive display. In such transmissive
display, the polarization state of light passing through the liquid
crystal layer 110 can be changed to perform light and dark displays
by controlling the alignment of liquid crystal in the liquid
crystal layer 110 by the electrodes 106 and 112.
[0068] In the reflective display mode of these display modes,
incident light passes through the liquid crystal layer 110 twice.
In the transmissive display mode, light emitted from the backlight
(illumination means) passes through the liquid crystal layer 110
only once. The retardation of the liquid crystal layer 110 will now
be considered. In a case in which alignment control is exerted by
applying the same voltage from the electrodes in a reflective
display mode and a transmissive display mode, the retardation of
liquid crystal differs, and the transmittance of liquid crystal is
thereby changed. However, in this embodiment, a
liquid-crystal-layer thickness control layer 109 made of acrylic
resin can be provided in a region where reflective display is
performed, that is, in a reflective display region having the
reflective electrode 108 shown in FIG. 1. Therefore, the thickness
of the liquid crystal layer 110 is larger in a transmissive display
region where transmissive display is performed than in the
reflective display region, and the states of the liquid crystal
layer 110 concerning the transmissive display and the reflective
display in the reflective display region and the transmissive
display region, that is, the distances by which light passes
through the liquid crystal layer 110 in the regions can be
optimized. Consequently, the liquid-crystal-layer thickness control
layer 109 made of acrylic resin allows the retardation to be
optimized in the reflective display region and the transmissive
display region, and permits bright and high-contrast reflective
display and transmissive display.
[0069] The retardation film 103 exhibits a positive uniaxiality
(nx2>ny2.apprxeq.nz2), and the retardation in the XY plane is
approximately 140 nm. The X-axis of the retardation film 103 is at
an angle of approximately 45.degree. to a polarization axis 101 of
the polarizer 102. The retardation film 115 exhibits a positive
uniaxiality (nx4>ny4.apprxeq.nz4), and the retardation in the XY
plane is approximately 140 nm. The X-axis of the retardation film
115 is at an angle of approximately 45.degree. to a polarization
axis 117 of the polarizer 116. The polarization axis 101 of the
polarizer 102 and the polarization axis 117 of the polarizer 116
are orthogonal to each other, and the X-axis of the retardation
film 103 and the X-axis of the retardation film 115 are similarly
orthogonal to each other. Since the phase difference between the
polarizers 102 and 116 can be made zero during non-driving time by
setting the retardation of the retardation film 103 equal to the
retardation of the retardation film 115, an ideal black display can
be achieved.
[0070] The retardation film 104 exhibits a negative uniaxiality
(nx1.apprxeq.ny1>nz1), and has a retardation of approximately 0
in the XY plane and a retardation of approximately 120 nm in the
Z-axis direction. The retardation film 114 exhibits a negative
uniaxiality (nx3.apprxeq.ny3>nz3), and has a retardation of
approximately 0 in the XY plane and a retardation of approximately
120 nm in the Z-axis direction. The liquid crystal layer 110
provides a retardation of 380 nm in the transmissive display region
and a retardation of 200 nm in the reflective display region. By
placing the retardation films 104 and 114, the phase difference of
the liquid crystal layer 110 made when viewed from the oblique
direction can be compensated for.
[0071] FIG. 12 is an explanatory view showing the action of
compensation for the viewing-angle characteristic. Light 10
obliquely emitted from the backlight (not shown) reaches a viewer
(not shown) through the third retardation film 114, the liquid
crystal layer 110, and the first retardation film 104. Since liquid
crystal molecules 110a are vertically aligned in the liquid crystal
layer 110, the retardation in the XY plane of the liquid crystal
layer 110 is approximately 0. The retardations in the XY plane of
the first retardation film 104 and the third retardation film 114
are also approximately 0. Therefore, the light 10 does not produce
a phase difference in the vertical direction. However, when light
obliquely enters, a phase difference is produced in the Z-axis
direction. Accordingly, a phase difference produced in the liquid
crystal layer 110 when obliquely viewed can be compensated for by
placing the retardation films 104 and 114.
[0072] FIG. 7 shows the relationship between W1/Rt and the
transmissive-display viewing range. FIG. 7(a) shows a case in which
the retardation Rt in a transmissive display region is 300 nm, and
FIG. 7(b) shows a case in which the retardation Rt in the
transmissive display region is 500 nm. The total retardation W1 in
the Z-axis direction is the sum of the retardation
(nx1-nz1).times.d1 in the Z-axis direction of the first retardation
film 104, the retardation (nx3-nz3).times.d3 in the Z-axis
direction of the third retardation film 114, the retardation
((nx2+ny2)/2-nz2).times.d2 in the Z-axis direction of the second
retardation film 103, and the retardation
((nx4+ny4)/2-nz4).times.d4 in the Z-axis direction of the fourth
retardation film 115. The transmissive-display viewing range means
a viewing range in which a high contrast of 30 or more can be
obtained. As shown in FIG. 7, the transmissive-display viewing
range takes the maximum value adjacent to Wt/Rt of 0.58.
[0073] FIG. 11 is a graph showing the relationship between the
backlight luminance and the polar angle in popular liquid crystal
display devices in portable telephones and the like. When the polar
angle is 0.degree., that is, when a display surface of a liquid
crystal display device is viewed from the vertical direction, the
backlight luminance is the highest. A high backlight luminance
(approximately 1000 cd/m.sup.2 or more) is obtained when the polar
angle is within the range of .+-.35.degree.. On the other hand, in
FIG. 7, a transmissive-display viewing range of 35.degree. or more
is obtained when 0.5.ltoreq.W1/Rt.ltoreq.0.75. Accordingly, high
contrast can be ensured above the range of the high backlight
luminance in the transmissive display region by setting the
retardation films so that 0.5.ltoreq.W1/Rt.ltoreq.0.75.
[0074] FIG. 10 shows the relationship between W4/Rr and a
reflective-display viewing range. FIG. 10 shows a case in which the
retardation Rr in the reflective display region is 200 nm. The
total retardation W4 in the Z-axis direction is the sum of the
retardation (nx1-nz1).times.d1 in the Z-axis direction of the first
retardation film 104, and the retardation
((nx2+ny2)/2-nz2).times.d2 in the Z-axis direction of the second
retardation film 103. The transmissive-display viewing range means
a viewing range in which a high contrast of 10 or more can be
obtained. In a known STN-mode liquid crystal display device, the
viewing range is approximately 30.degree.. On the other hand, in
FIG. 10, a transmissive-display viewing range of 30.degree. or more
is obtained when 0.5.ltoreq.W4/Rr.ltoreq.0.75. Accordingly, high
contrast can be ensured above the range of the viewing range of the
known STN-mode liquid crystal display device in the reflective
display region by setting the retardation films so that
0.5.ltoreq.W4/Rr.ltoreq.0.75.
[0075] The retardation films 103 and 115 may be broadband
quarter-wave plates each formed by appropriately combining a
half-wave plate and a quarter-wave plate. Preferably, in the
retardation films 103 and 115, the ratio R(450)/R(590) of the
retardation R(450) in the XY plane at 450 nm and the retardation
R(590) in the XY plane at 590 nm is less than 1. This makes it
possible to produce substantially circularly polarized light in the
visible region.
[0076] As described above, the liquid crystal display device of the
first embodiment can achieve a high-contrast display with a wide
viewing angle.
[0077] A second embodiment of the present invention will be
described below with reference to FIG. 2. The same reference
numerals as those in the first embodiment shown in FIG. 1 denote
similar structures, unless otherwise specified, and descriptions
thereof are omitted.
[0078] In order to perform reflective display, light incident from
the outside of the device is used, and the incident light is guided
to a liquid crystal layer 110 through a polarizer 102, retardation
films 103 and 104, an upper substrate 105, and an electrode 106. In
a reflective display region, the incident light passes through the
liquid crystal layer 110, and is then reflected by a reflective
electrode 108. The reflected light passes through the liquid
crystal layer 110 again, is returned to the outside of the device
through the electrode 106, the upper substrate 105, the retardation
films 104 and 103, and the polarizer 102, and reaches a viewer,
thereby performing reflective display. In such reflective display,
the polarization state of light passing through the liquid crystal
layer 110 can be changed to perform light and dark displays by
controlling the alignment of liquid crystal in the liquid crystal
layer 110 by the electrodes 106 and 112.
[0079] In order to perform transmissive display, light emitted from
a backlight (illuminationdevice) enters through a polarizer 116, a
retardation film 115, and a substrate 113. In this case, in a
transmissive display region, light incident from the substrate 113
passes through an electrode 112, the liquid crystal layer 110, the
electrode 106, the substrate 105, the retardation films 104 and
103, and the polarizer 102 in that order to perform transmissive
display. In such transmissive display, the polarization state of
light passing through the liquid crystal layer 110 can also be
changed to perform light and dark displays by controlling the
alignment of liquid crystal in the liquid crystal layer 110 by the
electrodes 106 and 112.
[0080] In the reflective display mode of these display modes,
incident light passes through the liquid crystal layer 110 twice.
In the transmissive display mode, light emitted from the backlight
(illumination device) passes through the liquid crystal layer 110
only once. The retardation of the liquid crystal layer 110 will now
be considered. In a case in which alignment control is exerted by
applying the same voltage from the electrodes in a reflective
display mode and a transmissive display mode, the retardation of
liquid crystal differs, and the transmittance of liquid crystal is
thereby changed. However, in this embodiment, a
liquid-crystal-layer thickness control layer 109 made of acrylic
resin is provided in a region where reflective display is
performed, that is, in the reflective display region having the
reflective electrode 108 shown in FIG. 2. Therefore, the thickness
of the liquid crystal layer 110 is larger in the transmissive
display region where transmissive display is performed than in the
reflective display region, and the states of the liquid crystal
layer 110 concerning the transmissive display and the reflective
display in the reflective display region and the transmissive
display region, that is, the distances by which light passes
through the liquid crystal layer 110 in the regions can be
optimized. Consequently, the liquid-crystal-layer thickness control
layer 109 made of acrylic resin allows the retardation to be
optimized in the reflective display region and the transmissive
display region, and permits bright and high-contrast reflective
display and transmissive display.
[0081] The retardation film 103 exhibits a positive uniaxiality
(nx2>ny2.apprxeq.nz2), and the retardation thereof in the XY
plane is approximately 140 nm. The X-axis of the retardation film
103 is at an angle of approximately 45.degree. to a polarization
axis 101 of the polarizer 102. The retardation film 115 exhibits a
positive uniaxiality (nx4>ny4.apprxeq.nz4), and the retardation
thereof in the XY plane is approximately 140 nm. The X-axis of the
retardation film 115 is at an angle of approximately 45.degree. to
a polarization axis 117 of the polarizer 116. The polarization axis
101 of the polarizer 102 and the polarization axis 117 of the
polarizer 116 are orthogonal to each other, and the X-axis of the
retardation film 103 and the X-axis of the retardation film 115 are
similarly orthogonal to each other. Since a phase difference
between the polarizers 102 and 116 can be made zero during
non-driving time by setting the retardation of the retardation film
103 equal to the retardation of the retardation film 115, an ideal
black display can be achieved.
[0082] The retardation film 104 exhibits a negative uniaxiality
(nx1.apprxeq.ny1>nz1), and has a retardation of approximately 0
in the XY plane and a retardation of approximately 220 nm in the
Z-axis direction. The liquid crystal layer 110 provides a
retardation of 380 nm in the transmissive display region. By
placing the retardation film 104, a phase difference of the liquid
crystal layer 110 produced when viewed from the oblique direction
can be compensated for.
[0083] FIG. 8 shows the relationship between W2/Rt and the
transmissive-display viewing range. FIG. 8 shows a case in which
the retardation Rt in the transmissive display region is 400 nm.
The total retardation W2 in the Z-axis direction is the sum of the
retardation (nx1-nz1).times.d1 of the first retardation film 104,
the retardation ((nx2+ny2)/2-nz2).times.d2 of the second
retardation film 103, and the retardation
((nx4+ny4)/2-nz4).times.d4 of the fourth retardation film 115. The
transmissive-display viewing range means a viewing range in which a
high contrast of 30 or more can be obtained. As shown in FIG. 11, a
high backlight luminance (approximately 1000 cd/m.sup.2 or more) is
obtained when the polar angle is within the range of
.+-.35.degree.. On the other hand, as shown in FIG. 8, a
transmissive-display viewing range of 35.degree. or more is
obtained when 0.5.ltoreq.W2/Rt.ltoreq.0.75. Accordingly, high
contrast can be ensured above the range of the high backlight
luminance in the transmissive display region by setting the
retardation films so that 0.5.ltoreq.W2/Rt.ltoreq.0.75.
[0084] As described above, the liquid crystal display device of the
second embodiment can achieve a high-contrast display with a wide
viewing angle.
[0085] A third embodiment of the present invention will be
described below with reference to FIG. 3. The same reference
numerals as those in the first embodiment shown in FIG. 1 denote
similar structures, unless otherwise specified, and descriptions
thereof are omitted.
[0086] In order to perform reflective display, light incident from
the outside of the device is used, and the incident light is guided
to a liquid crystal laser 110 through a polarizer 102, a
retardation film 103, an upper substrate 105, and an electrode 106.
In a reflective display region, the incident light passes through
the liquid crystal layer 110, and is then reflected by a reflective
electrode 108. The reflected light passes through the liquid
crystal layer 110 again, is returned to the outside of the device
through the electrode 106, the upper substrate 105, the retardation
film 103, and the polarizer 102, and reaches a viewer, thereby
performing reflective display. In such reflective display, the
polarization state of light passing through the liquid crystal
layer 110 can also be changed to perform light and dark displays by
controlling the alignment of liquid crystal in the liquid crystal
layer 110 by the electrodes 106 and 108.
[0087] In order to perform transmissive display, light emitted from
a backlight (illumination device) enters through a polarizer 116,
retardation films 115 and 114, and a substrate 113. In this case,
in a transmissive display region, the light incident from the
substrate 113 passes through an electrode 112, the liquid crystal
layer 110, the electrode 106, the substrate 105, the retardation
film 103, and the polarizer 102 in that order to perform
transmissive display. In such transmissive display, the
polarization state of light passing through the liquid crystal
layer 110 can also be changed to perform light and dark displays by
controlling the alignment of liquid crystal in the liquid crystal
layer 110 by the electrodes 106 and 112.
[0088] In the reflective display mode of these display modes,
incident light passes through the liquid crystal layer 110 twice.
In the transmissive display mode, light emitted from the backlight
(illumination device) passes through the liquid crystal layer 110
only once. The retardation of the liquid crystal layer 110 will now
be considered. In a case in which alignment control is exerted by
applying the same voltage from the electrodes in a reflective
display mode and a transmissive display mode, the retardation of
liquid crystal differs, and the transmittance of liquid crystal is
thereby changed. However, in this embodiment, a
liquid-crystal-layer thickness control layer 109 made of acrylic
resin is provided in a region where reflective display is
performed, that is, in the reflective display region having the
reflective electrode 108 shown in FIG. 3. Therefore, the thickness
of the liquid crystal layer 110 is larger in the transmissive
display region where transmissive display is performed than in the
reflective display region, and the states of the liquid crystal
layer 110 concerning the transmissive display and the reflective
display in the reflective display region and the transmissive
display region, that is, the distances by which light passes
through the liquid crystal layer 110 in the regions can be
optimized. Consequently, the liquid-crystal-layer thickness control
layer 109 made of acrylic resin allows the retardation to be
optimized in the reflective display region and the transmissive
display region, and permits bright and high-contrast reflective
display and transmissive display.
[0089] The retardation film 103 exhibits a positive uniaxiality
(nx2>ny2.apprxeq.nz2), and the retardation thereof in the XY
plane is approximately 140 nm. The X-axis of the retardation film
103 is at an angle of approximately 45.degree. to a polarization
axis 101 of the polarizer 102. The retardation film 115 exhibits a
positive uniaxiality (nx4>ny4.apprxeq.nz4), and the retardation
thereof in the XY plane is approximately 140 nm. The X-axis of the
retardation film 115 is at an angle of approximately 45.degree. to
a polarization axis 117 of the polarizer 116. The polarization axis
101 of the polarizer 102 and the polarization axis 117 of the
polarizer 116 are orthogonal to each other, and the X-axis of the
retardation film 103 and the X-axis of the retardation film 115 are
similarly orthogonal to each other. Since the phase difference
between the polarizers 102 and 116 can be made zero during
non-driving time by setting the retardation of the retardation film
103 equal to the retardation of the retardation film 115, an ideal
black display can be achieved.
[0090] The retardation film 114 exhibits a negative uniaxiality
(nx3.apprxeq.ny1>nz3), and has a retardation of approximately 0
in the XY plane and a retardation of approximately 240 nm in the
Z-axis direction. The liquid crystal layer 110 provides a
retardation of 380 nm in the transmissive display region. By
placing the retardation film 114, a phase difference of the liquid
crystal layer 110 produced when viewed from the oblique direction
can be compensated for.
[0091] FIG. 9 shows the relationship between W3/Rt and the
transmissive-display viewing range. FIG. 9 shows a case in which
the retardation Rt in the transmissive display region is 380 nm.
The total retardation W3 in the Z-axis direction is the sum of the
retardation (nx3-nz3).times.d3 of the third retardation film 114,
the retardation ((nx2+ny2)/2-nz2).times.d2 of the second
retardation film 103, and the retardation
((nx4+ny4)/2-nz4).times.d4 of the fourth retardation film 115. The
transmissive-display viewing range means a viewing range in which a
high contrast of 30 or more can be obtained. As shown in FIG. 11, a
high backlight luminance (approximately 1000 cd/m.sup.2 or more) is
obtained when the polar angle is within the range of
.+-.35.degree.. On the other hand, as shown in FIG. 9, a
transmissive-display viewing range of 35.degree. or more is
obtained when 0.5.ltoreq.W3/Rt.ltoreq.0.75. Accordingly, high
contrast can be ensured above the range of the high backlight
luminance in the transmissive display region by setting the
retardation films so that 0.5.ltoreq.W3/Rt.ltoreq.0.75.
[0092] As described above, the liquid crystal display device of the
third embodiment can achieve a high-contrast display with a wide
viewing angle.
[0093] Examples of electronic devices equipped with the liquid
crystal display devices of the above embodiments will be
described.
[0094] FIG. 4 is a perspective view showing an example of a
portable telephone. In FIG. 4, reference numerals 1000 and 1001
denote a main body of the portable telephone, and a liquid crystal
display using the liquid crystal display devices of the
above-described first to third embodiments.
[0095] FIG. 5 is a perspective view showing an example of a
wristwatch-type electronic device. In FIG. 5, reference numerals
1100 and 1101 denote a main body of the wristwatch, and a liquid
crystal display using the liquid crystal display devices of the
above-described first to third embodiments.
[0096] FIG. 6 is a perspective view showing an example of a
portable information processor, such as a word processor or a
personal computer. In FIG. 6, reference numerals 1200, 1202, 1204,
and 1206 respectively denote an information processor, an input
section such as a keyboard, a main body of the information
processor, and a liquid crystal display using the liquid crystal
display devices of the above-described first to third
embodiments.
[0097] Since the electronic devices shown in FIGS. 4 to 6 have a
liquid crystal display using the liquid crystal display devices of
the above-described first to third embodiments, they can provide a
wide viewing angle and high contrast in various environments.
[0098] As described in detail above, according to the present
invention, it is possible to achieve high-contrast reflective and
transmissive display with a wide viewing angle in a transflective
liquid crystal display device having both reflective and
transmissive structures.
* * * * *